An indirect heat transfer type grooved agitating dryer is known as a heat exchange device for drying, heating or cooling a variety of powder and granular materials.
The device disclosed in, for example, Japanese Examined Patent Application Publication No. S48-44432 (Patent Literature 1, hereinafter) is known as such device.
In the device disclosed in Patent Literature 1, a shaft, having a plurality of heat exchangers disposed at predetermined intervals, is rotatably supported within a horizontally long casing. A heat exchange medium is supplied into the heat exchangers via the shaft, and the heat exchangers are rotated within the casing. This device is structured such that a powder and granular material is dried (heated, cooled) by indirect heat transferred from the shaft and heat exchangers.
Each of the heat exchangers disclosed in Patent Literature 1 has a structure shown in FIG. 11. The heat exchanger is a wedge-shaped hollow rotating body 50. The wedge-shaped hollow rotating body 50 is formed by joining two pieces of fan-shaped plate materials 51, 51 into contact with each other at one side of their ends while separating the fan-shaped plate materials 51, 51 at the other side of their ends, to block the periphery thereof with plate materials 52, 53. Therefore, the hollow rotating body 50 is shaped into a wedge in which a front end part 54 at the tip end in a rotation direction forms a line, while a rear end part 55 at the rear end in the rotation direction forms a surface. The device disclosed in Patent Literature 1 uses two of the wedge-shaped hollow rotating bodies 50 as a pair. In other words, these two wedge-shaped hollow rotating bodies 50 are disposed at symmetrical positions on a shaft 60 with certain gaps A, A therebetween, as shown in FIG. 12. Then a plurality of pairs of the two wedge-shaped hollow rotating bodies 50 are disposed at predetermined intervals in an axial direction of the shaft 60.
The indirect heat transfer type grooved agitating dryer disclosed in Patent Literature 1 had the following excellent characteristics:
(1) Small installation area, and small in size.
(2) Large heat transfer coefficient, and high heat efficiency.
(3) Self-cleaning effect achieved by the wedge-shaped hollow rotating bodies.
(4) The temperature of an object to be processed and the time for processing it can be controlled easily.
(5) Powder and granular material with high moisture content can be processed as well.
(6) Excellent piston flowability (transferability) of the object to be processed.
The device described in Patent Literature 1, however, had the following problems:
(a) The object to be processed adheres/accumulates in the angled parts other than the diagonal plate surface of the wedge of the heat exchanger, particularly in a section where the shaft and the wedge-shaped heat exchanger are attached. Adhesion/accumulation of the object to be processed reduces the heat-transfer area of the heat exchanger, lowering the heat efficiency of the device. Moreover, the adhered/accumulated object to be processed falls off of the heat exchanger as time advances, causing, in some cases or according to the heat history, different types of block objects to be mixed into the object to be processed.
(b) The production of the shaft provided with the wedge-shaped hollow rotating bodies requires an enormous amount of time. In other words, each wedge-shaped hollow rotating body 50 is fabricated by disposing the two pieces of fan-shaped plate materials 51, 51, an isosceles triangular plate material 52, and a trapezoidal plate material 53 in the manner shown in FIG. 13 and welding the entire periphery of the abutment parts between these materials. Therefore, when forming a single heat exchanger, there are many steps in the welding process alone, and automation of the welding operation is difficult. Furthermore, when fixing each of the obtained heat exchangers to the shaft 60, plate material 61 formed with cutout holes which are substantially the same shape as a part (opening) of each heat exchanger that is in contact with the shaft 60, is lined (welded) on the entire outer peripheral surface of the shaft 60, and thereafter the plate material 61, the shaft 60 and the parts of the heat exchangers abutting on the plate material 61 and the shaft need to be welded at the entire periphery of the abutting sections. In addition, in such welding, the welding methods of each layer need to be changed. For this reason, the problem of the device described in Patent Literature 1 is that an enormous amount of time is required in fabricating the heat exchangers.
There is also a device in which hollow disks are simply attached as heat exchangers to a shaft. The heat exchanger with such a configuration, however, cannot ensure the piston flowability of the object to be processed, which are the excellent characteristic of the wedge-shaped hollow rotating body disclosed in Patent Literature 1. This is because the piston flowability of the object to be processed can be ensured for the first time by allowing the object to be processed to pass regularly through the gaps A, A of the two wedge-shaped hollow rotating bodies 50, 50 attached to the shaft 60. Here, the piston flowability are important factors for realizing the first-in-first-out phenomenon of the object to be processed, as well as for obtaining residence time, heat history, reaction time and the like to keep each particle of the powder/granular even. The piston flowability are also important attributes of the heat exchange device in order to maintain the consistent quality of the object to be processed.
The gaps A, A described in Patent Literature 1 function to transfer a powder and granular material layer, which is formed at the nearest part (upstream side) within the device, from a raw material feeding port side to a product discharge side, in a manner that each wedge-shaped hollow rotating body 50 that is rotated by the rotation of the shaft cuts out the powder and granular material layer. At this moment, the wedge-shaped hollow rotating body 50 itself does not have an extrusion force that a screw has. For this reason, the powder and granular material is sliced regularly, such as twice per rotation, in order to be transferred by the gaps A, A simply using the pressure of the powder and granular material. Therefore, back mixing or short pass seldom occurs on the powder and granular material in this device, so that “the first-in-first-out phenomenon” can be ensured and the piston flowability can be realized. On the other hand, in the case of simple hollow disk-shaped rotating bodies, the object to be processed is transferred from a gap between a casing and each rotating body to a downstream side. As a result, the back mixing or short pass phenomenon occurs where a part of the powder and granular material layer in the vicinity of the shaft remains in its position, while a part of the same near the casing moves rapidly. Thus, in the case of such simple hollow disk-shaped rotating bodies, the piston flowability cannot be realized.